1. Field of the Invention
This invention generally relates to a capacitor used in an electronic device and a manufacturing method of the same.
2. Description of the Related Art
Recently, there are demands for enhancing capacitance of a capacitor, for downsizing the capacitor, for lowering electrical power consumption of the capacitor and for lowering impedance at high frequencies of the capacitor, as electronics devices are digitalized. A roll-formed electrolytic capacitor is known. The capacitor has a structure in which a capacitor element is packaged in a case such as aluminum case or a resin case having a cylindrical shape and having a bottom, and an opening of the case is sealed.
Japanese Patent Application Publication No. 2000-114118 (hereinafter referred to as Document 1) and Japanese Patent Application Publication No. 11-3840 (hereinafter referred to as Document 2) disclose a method of putting an epoxy resin or a method of resistance welding with use of an airtight metal, as the sealing method. And the opening is sealed with a sealing material such as a rubber, because the rubber is inexpensive, has sealing activity and has humidity resistance.
It is necessary to reduce a leakage current from the capacitor as much as possible, because there is a demand for lowering the electrical power consumption of the capacitor. And so, a tab terminal is welded to the electrode foil and a rolled element is energized in an electrolytic solution. The electrode foil and the tab terminal are subjected to a chemical conversion treatment. And the leakage current is reduced. Japanese Patent Application Publication NO. 2001-284175 (hereinafter referred to as Document 3) discloses a method of coating an insulating resin to the tab terminal.
However, a load intends to be applied to the terminal when the resin is enclosed or the resistance welding is processed, in accordance with the arts of Document 1 and Document 2. Effect of coated layer is reduced because the sealing material limits impregnation of the electrolytic solution to the electrode foil and the terminal, when a chemical coated layer is formed on the electrode foil and the terminal. And a pressure applied to the electrode foil and the terminal breaks the chemically treated layer when the sealing material is put into, in a case where the sealing material is put into after the coated layer is formed. And it is possible that the leakage current is increased. The same goes for the art of Document 3.
There is a case where the capacitor is subjected to a heat of more than 200 degrees C. as in the case of soldering reflow for few seconds to few minutes. In this case, it is possible that the leakage current is increased and defective appearance is brought about by the deformation of the sealing material, because the inner pressure is increased by the decomposition of the electrolyte and a pressure is applied to the element by the expansion of the sealing material.